We personally don't participate in RPs about educational institutions, but we can also see how many enjoy them. For us, such RPs wouldn't be the sort we find easy to join, as we've not attended any sort of school in a good while.

The overflow RP type tends to vary over time, with no clear schedule or duration for each set. One month it might be schools, the next week it might be post-apocalyptic. Sometimes, these tend to blend together. But we also noted last year around the release of Star Wars Episode VII that RPs related to that (to varying degrees) were very popular. No doubt there were also numerous Game of Thrones-esque RPs around when that ran back before the summer.

We know the reasons behind such popularities are very much based around the inscruitable interests of the individual members, which is why there is no clear pattern to what is popular when. We do have a prediction that Star Wars will get another boost around the release of Rogue One, though.